Bubbles Go High-Tech to Fight Tumours

The process of blocking blood flow to a tumour is called embolisation, and using gas bubbles is a new technique in embolotherapy. What makes it so promising is that the technique allows doctors to control exactly where the bubbles are formed, so blockage of blood flow to surrounding tissue is minimal, said Joseph Bull, assistant professor of biomedical engineering at U-M.

The research of Bull and collaborator Brian Fowlkes, an associate professor in the Department of Radiology in the U-M Medical School, is currently focused on the fundamental vaporisation and transport topics that must first be understood in order to translate this developmental technique to the clinic. Gas bubbles allow very precise delivery because their formation can be controlled and directed from the outside, by a focused high intensity ultrasound.

This envisioned technique is actually a two-step process, Bull said. First, a stream of encapsulated superheated perfluorocarbon liquid droplets goes into the body by way of an intravenous injection. The droplets are small enough that they don’t lodge in vessels. Doctors image the droplets with standard ultrasound, and once the droplets reach their destination, scientists hit them with high intensity ultrasound. The ultrasound acts like a pin popping a water balloon. After the shell pops, the perfluorocarbon expands into a gas bubble that is approximately 125 times larger in volume than the droplet.

"If a bubble remained spherical its diameter would be much larger than that of the vessel," Bull said. "So it deforms into a long sausage-shaped bubble that lodges in the vessel like a cork. Two or three doses of bubbles will occlude most of the (blood) flow." Without blood flow, the tumour dies.